1. Field of the Invention
The present invention relates, in general, to determining and monitoring whether fasteners such as bolts are properly tightened, e.g., are under a proper pre-load or torque, and, more particularly, to fasteners or other structural members/components that are adapted for remote monitoring of torque or other physical characteristics indicative of a particular tensile or compressive load and to systems and methods for performing such remote monitoring of the fasteners. The present invention facilitates monitoring of numerous fasteners that have been installed in an apparatus, assembly, system, or product in an efficient and timely manner.
2. Relevant Background
To ensure safety and proper ongoing operations, the methods of joining parts into a structural assembly or system are extremely important. Typical methods of joining or fastening parts include the use of such items as bolts, nuts, cap screws, set screws, rivets, and other structural members, and in a typical structural assembly or product, each of these fasteners has its material, size, and other physical characteristics carefully selected to ensure the structural integrity of the assembly or product. For example, a jumbo jet may require as many as 2 million fasteners, and each of these must be properly selected, sized, and installed. Fasteners are an important design feature for a wide range of applications such as trains, subways, airplanes, ships, bridges, automobiles, power and processing plants, and numerous consumer products.
Many fasteners are utilized in applications where vibration, varying loads, and other operating parameters can cause the fasteners to loosen. For example, fasteners such as nuts and bolts may be used in many assemblies to create frictional forces and provide structure that allow the fasteners to carry a particular load (i.e., design loads). Such loading or pre-loading of the fasteners can typically vary with a range of loads but needs to be retained above a defined minimum to ensure that the integrity of the structural assembly is maintained based on its engineering design. The basis for such designs is that the load or clamp load of the fastener is maintained throughout its lifecycle or during its use. In the nut and bolt example, the fastener is used to join two parts of an assembly by threading the nut and bolt together and applying a particular torque (or torque value or tensile pre-load within a preset range) on the nut which applies a tensile force to the bolt causing it to elongate or become longer. Since the torque may vary over time, many uses of fasteners require that the torque or tightness of a fastener be periodically checked or verified to ensure safe use or to reduce the risk of the part or assembly failing (e.g., becoming unfastened).
As a particular illustration, a large number of bolts are used as fasteners in roller coasters and other rides of an amusement park. These bolts may be used to attach bogeys or wheels to the cars and for other structural components. Many of these bolts must be tightened to or above a certain torque value or pre-load based on the design of the ride or ride equipment or the design of the fastener to be effective for its purpose. Once this torque value is obtained, operating or safety procedures may require that the fasteners be at least periodically checked to verify the bolts remain properly tightened. For a relatively basic ride, this may involve inspecting hundreds or even thousands of fasteners.
The most common method of checking fasteners involves the manual inspection of each and every fastener. Visual inspection methods may involve pre-loading or initially torquing a fastener to a desired point and then, painting a thin alignment stripe down the bolt's or the nut's edge and adjacent equipment. When the fastener loosens or moves out of the desired torque range, the alignment is lost. Other inspection methods may include use of torque wrenches, use of feeler gauges (and/or torque indicating washers), and inspection of torque rings. These manual inspection techniques are time consuming, tedious, and sometimes difficult to perform properly (e.g., access may require the use of mirrors on extensions or the like). Manual inspection is also more prone to error. Additionally, engineers often design a ride or other product assembly so as to allow manual or visual inspection, which sometimes results in less desirable designs or at least designs that differ from those where inspection is not required. Efforts to automate torque monitoring typically involve using strain gauges that are linked to computers. These automated systems are typically expensive and relatively complex and require power be provided at or near the fastener, and as a result, these systems have not been widely adopted and are not suited for many assemblies or products. e.g., moving vehicles such as roller coaster cars, trains, or the like, with large nunbers of fasteners.
There remains a need for systems for monitoring fasteners to verify their tightness or an applied torque or load and for fasteners adapted for use in such systems. Preferably, such systems and fasteners would be configured to allow remote monitoring of the fasteners in an effective and timely manner, e.g., to monitor torque or load applied to bolts or other fasteners without visual inspection.